Battery Pack and Battery Protection Method

ABSTRACT

A battery protection operation having higher safety is performed in a battery pack. Presence/absence of plural abnormal states including at least an overcharge state and an overdischarge state based on detected results of voltage between a positive terminal and a negative terminal of a battery cell as well as an overcurrent charge state and an overcurrent discharge state indicating that charge current and discharge current are excessive respectively based on detected results of charge and discharge current of the battery cell are determined at any time and an abnormality determination flag showing a determination result of respective abnormal states as a flag is stored. In addition, control states A to D according to combinations of respective operation states of the a discharge current shut-off circuit selectively shutting off discharge current of the battery cell and a charge current shut-off circuit selectively shutting off charge current of the battery cell are defined, and to which control state the state should be changed will be determined based on a value of the abnormality determination flag.

TECHNICAL FIELD

The invention related to a battery pack in which a processing circuitexecuting protection processing for occurrence of abnormality of asecondary battery is housed with the secondary battery, and a batteryprotection method for protecting the secondary battery.

BACKGROUND ART

In recent years, portable electronic apparatuses such as a digital videocamera are increasing, and performance of secondary batteries mounted onthese electronic apparatuses is regarded as important. As one of suchsecondary batteries, there is one called a lithium-ion type.

In portable electronic apparatuses using the secondary batteries aspower supply, there are many ones that a battery remaining amountdisplay function is installed. Particularly, a lithium-ion secondarybattery has a characteristic that battery cell voltage decreases slowlyand linearly except a period just after the start of discharge and aperiod just before the completion of discharge, therefore, the batteryremaining amount can be predicted relatively accurately and can bedisplayed. To predict the remaining amount more accurately, it ispreferable to detect integrated values of charge and discharge current,temperature of the battery cell and the like in addition to thedetection of the battery cell voltage. A battery pack in which a circuitsuch as a microcomputer to perform such detection or calculation ishoused with the lithium-ion type battery cell in the same package iscommercially available, in which the function of accurate remainingamount display is realized by reading out the detection/calculationinformation of the battery pack.

In the lithium-ion secondary battery, it is known that lithium ionbecomes metal lithium and is precipitated at an anode especially at thetime of overcharge, and smoke or fire may occur from the battery or thebattery is exploded at the worst case. At the time of overdischarge, itis also known that small short-circuit or capacity loss occurs insidethe battery at the time of overdischarge, and abnormal heat generationoccurs by overcurrent flowing when a cathode and an anode are shortcircuited. Accordingly, the lithium-ion secondary battery is usuallyprovided with a protection function monitoring these abnormal states anda switch for avoiding the abnormal states in order to preventovercharge, overdischarge and short-circuit (over current).

Specifically, the switch is realized as two FETs (Field EffectTransistors) in which propriety of charging and discharging of thebattery cell can be controlled respectively. The operations of theseFETs are controlled by a control circuit such as a microcontrolleraccording to detected values of voltage at both ends of the battery cellor current. The control circuit and the FETs for protection operationsare also housed in the battery pack with the battery cell.

As a conventional battery pack having the above function, there was onein which the protection function of the battery cell is realized by acircuit including a dedicated voltage comparator as a main component(for example, refer to Japanese Patent 31336677, paragraph number [0011]to [0016], FIG. 1). In addition, in order to realize the protectionfunction chiefly by software control, there was a battery pack in whichplural control states indicating charge states and discharge states ofthe battery cell are defined in advance and these control states aredetermined based on detected values of voltage at both ends of thebattery cell and discharge current, then, operations of protection FETsare controlled according to the control states (for example,JP-A-2005-151696, paragraph number [0084] to [0101], FIG. 8),

FIG. 9 is a view showing transition examples of control states in theconventional battery pack.

In the battery back disclosed in the JP-A-2005-151696, five controlstates which are an overcharge state, a normal state, an overdischargestate, a deep discharge state and an overcurrent state are defined asshown in FIG. 9, and the operations of a FET for charge control and aFET for discharge control (denoted as a charge FET and a discharge FETrespectively in the drawing) are determined in each control state. Inthe FET for charge control and the FET for discharge control, chargecurrent and discharge current are shut off by turning off the FETs.

The transitions among the overcharge state, the normal state, theoverdischarge state and the deep discharge state are controlled based onthe detected results of the battery cell voltage. In the normal state,both FETs for charge control and for discharge control are turned on,and charging from a charger as well as discharging, namely, power supplyto the apparatus are possible. When the battery cell voltage becomesmore than a certain value (in this case, 4.20V or more), the normalstate makes a transition to the overcharge state, and the FET for chargecontrol is turned off to prevent occurrence of abnormality due toovercharge. When the battery cell voltage decreases to less than acertain value (in this case, less than 4.10V) after that, the statereturns to the normal state.

When the battery cell voltage further decreases less than a certainvalue (in this case, less than 2.50V), the normal state makes atransition to the disovercharge state, and the FET for discharge controlis turned off, which disables power supply to the apparatus. In theoverdischarge state, when the battery cell voltage increases to acertain value (in this case, 2.52V or more), the state returns to thenormal state, which enables power supply again. However, when thebattery cell voltage further decreases to less than a certain value (inthis case, less than 2.20V), the over discharge state makes a transitionto the deep discharge state. In the deep discharge state, the controlcircuit for protection operation is not able to be operated due to thevoltage decrease, and the control circuit is shut down. When thecharging is started and the battery cell voltage increases to a certainvalue (in this case, 2.50V or more), the operation of the controlcircuit is started and the state makes a transition to the overdischargestate.

In the conventional battery pack, not only the battery cell voltage butalso discharge current of the battery cell is detected, which preventsabnormality occurrence such as heat generation caused by excessivecurrent flowing due to short circuit between positive and negativeterminals. In FIG. 9, in the normal state and the overcharge state inwhich the FET for discharge control is on, when the discharge currentbecomes more than a certain value (in this case, 3.0 A or more), thestate makes a transition to an overcurrent state, and the FET fordischarge control is turned off. In this state, when the FET for chargecontrol is turned on and the start of charging is detected by thevoltage detection at a charge terminal and the like, the state makes atransition to the normal state.

In the overcurrent state, a method of returning by detecting thatdischarge load is released can be considered, however, there is a casethat a situation occurs, in which the overcurrent state and the normalstate are repeated by contact/non-contact between metal such as a keyand an electrode being repeated, therefore, the return is performed bythe charge detection in order to avoid the above situation.

As described above, chiefly in the case that overcharge or overcurrentoccurred, abnormality occurrence at the battery cell was prevented byallowing the control state to be changed according to the detectedvalues of the battery cell voltage and discharge current.

Recently, it is desired that battery protection processing which hasfurther higher safety is performed, assuming that various situationsaccording to the battery cell voltage or current. However, the aboveconventional battery cell protection method is insufficient for dealingwith all abnormal states accurately.

For example, in the conventional protection method of the battery cell,there is a problem that it is not always possible to perform appropriatecontrol processing such as in the case that plural abnormalities occur.As an example, in the case that abnormalities of overcharge andovercurrent occur simultaneously from the normal state, there is apossibility that it is not possible to determine that the state shouldbe changed to which control state in either the overcharge state or theovercurrent state, and it is not possible to perform

appropriate on/off operation of the FETs, as a result, it is notpossible to prevent either the charge voltage or discharge current frombeing excessive. In order to avoid the situation, it is desired thatcontrol states and state transition conditions according to the batterycell voltage and discharge current are defined more accurately andclearly, however, there is a problem that control processing will becomplicated as these are defined accurately.

Also there is a problem that it is not possible to determine thattransition is whether from the normal state or from the overcharge statewhen the state makes a transition to the overcurrent state. There is acase, for example, that battery cell voltage at the time of return fromthe overcurrent state differs according to the transition from whichstate, therefore, a case in which control becomes unnatural isconceivable, such that it is necessary to change the control state againaccording to the battery cell voltage at that time, if the overchargestate is allowed to return to the normal state uniquely. There is also aproblem that analysis of abnormality occurrence is not easy because itis not possible to immediately know from which state the state has beenchanged to the overcurrent state.

It is further desired to detect that not only discharge current but alsocharge current becomes excessive and to execute protection operationaccording to the detection. There is a problem that it is necessary todefine the control states or state transition conditions furtheraccurately for the above purpose and that the control processing will becomplicated.

In a battery pack in which two or more battery cells are housed, it isconceivable that a case in which abnormalities which are differentaccording to the battery cells, however, state transition consideringsuch case is not assumed, and there is a problem that appropriateprotection operation is not always executed.

The invention has been made in view of the above problems, and an objectthereof is to provide a battery pack in which battery protectionoperation having further higher safety.

Another object of the invention is to provide a battery protectionmethod which is capable of executing battery protection operation havingfurther higher safety.

DISCLOSURE OF THE INVENTION

In order to solve the above problems, in a battery pack in which aprocessing circuit executing protection processing for abnormalityoccurrence of a secondary battery is housed with the secondary battery,there is provided a battery pack including a discharge current shut-offcircuit selectively shutting off discharge current of the secondarybattery, a charge current shut-off circuit selectively shutting offcharge current of the secondary battery, a voltage detection unitdetecting voltage between a positive terminal and a negative terminal ofthe secondary battery, a current detection unit detecting magnitude ofcharge and discharge current of the secondary battery, an abnormal statedetermination unit

determining presence/absence of plural abnormal states at any time,which include at least an overcharge state and an overdischarge statebased on detected results by the voltage detection unit as well as anovercurrent charge state and an overcurrent discharge state indicatingthat charge current and discharge current are excessive respectivelybased on detected results by the current detection unit and storingdetermination information indicating a determination result at thattime, and a protection processing unit controlling respective operationsof the discharge current shut-off circuit and the charge currentshut-off circuit based on the determination information.

In the above battery pack, voltage between the positive terminal and thenegative terminal of the secondary battery is detected by the voltagedetection unit, and magnitude of charge and discharge current of thesecondary battery is detected by the current detection unit. In theabnormal state determination unit, presence/absence of plural abnormalstates including at least an overcharge state and an overdischarge statebased on detected results by the voltage detection unit as well as anovercurrent charge state and an overcurrent discharge state indicatingthat charge current and discharge current are excessive respectivelybased on detected results by the current detection unit are determinedat any time, and determination information indicating determinationresults at that time is stored. Accordingly, presence/absence of pluralabnormal states including the overcharge state, the overdischarge state,the overcurrent charge state and the overcurrent discharge state aremanaged independently. In the protection processing unit, respectiveshut-off/conductive operations of the respective discharge currentshut-off circuit and the charge current shut-off circuit are controlledbased in the determination information, therefore, appropriate controlof respective shut-off circuits according to presence/absence ofrespective abnormal states can be executed.

According to the battery back of the invention, presence/absence ofplural abnormal states including the overcharge state, the overdischargestate, the overcurrent charge state, the overcurrent discharge state aremanaged independently by the determination information stored in theabnormal state determination unit, therefore, the protection processingunit controlling the discharge current shutdown circuit and the chargecurrent shut-off circuit can positively execute appropriate controlaccording to presence/absence of respective abnormal states based on thedetermination information. Particularly, since the abnormal statedepending on voltage of the secondary battery and the abnormal statesdepending on charge current and discharge current respectively aremanaged individually by the determination information, the protectionprocessing unit can control respective shut-off circuits on conditionthat these abnormal states are recognized. Therefore, protectionoperation having higher safety can be realized.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing the whole configuration of a battery packaccording to a first embodiment of the invention.

FIG. 2 is a diagram showing an internal configuration of a batteryprotection circuit.

FIG. 3 is a view showing transitions of control states ofcharge/discharge operations by a microcontroller.

FIG. 4 is a diagram showing a configuration of an abnormalitydetermination flag.

FIG. 5 is a diagram showing correspondence between values of theabnormality flag and control states.

FIG. 6 is a diagram showing a configuration of a battery pack accordingto a second embodiment of the invention.

FIG. 7 is a diagram showing abnormality determination flagscorresponding to respective battery cells.

FIG. 8 is a chart showing transition conditions of control statesaccording to abnormal states of respective battery cells.

FIG. 9 is a view showing transition examples of control states accordingto a conventional battery pack.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments of the invention will be explained in detailwith reference to the drawings.

FIG. 1 is a diagram showing the whole configuration of a battery packaccording to a first embodiment of the invention.

A battery pack 1 shown in FIG. 1 houses a battery cell 2 including asecondary battery and a battery protection circuit 3 which realizes aprotection function with respect to abnormal states of the battery cell2 in one package. A positive terminal 21 and a negative terminal 22 ofthe battery cell 2 are respectively connected to a cell-side positiveterminal 31 and a cell-side negative terminal 32 of the batteryprotection circuit 3 by, for example, welding. An external positiveterminal 33 and an external negative terminal 34 of the batteryprotection circuit 3 are power supply terminals supplying power to anapparatus to be a discharge load such as a digital camera, as well asterminals for receiving power supply from an external charger.

A control terminal 35 for performing communication with the apparatus tobe the discharge load is also provided at the battery protection circuit3. A present operation state and the like of the battery protectionfunction for verifying abnormality can be outputted through the controlterminal 35.

The battery protection circuit 3 has not only the protection function ofthe battery cell 2 but also a processing function for displaying aremaining amount of the battery cell 2. For example, as the processingfunction, a function of calculating an integrated value of current, thenumber of times of charging of the battery cell 2 is included. It ispossible that the calculated results are transmitted to the apparatusthrough the control terminal 35, and that the remaining amount of thebattery cell 2 is calculated accurately based on the receivedinformation at the side of the apparatus.

As the battery cell 2, for example, a secondary battery of a lithium-iontype and the like can be used. It becomes possible to detect remainingcapacity of the battery with high accuracy at the side of the apparatusand to display the battery remaining amount, for example, as availableremaining time by using the secondary battery having a dischargecharacteristic in which discharge voltage decreases relatively slowly aswell as linearly such as the lithium-ion secondary battery.

FIG. 2 is a diagram showing an internal configuration of a batteryprotection circuit.

As shown in FIG. 2, the battery protection circuit 3 includes amicrocontroller 110, a FET for charge control 121 and a FET fordischarge control 122 (hereinafter, referred to as the charge FET 121and the discharge FET 122) and a resistance R1 for current detection.The microcontroller 110 includes a CPU (Central Processing Unit) 111, adriver 112, a communication interface circuit 113, an A/D convertingcircuit 114 and a temperature detection circuit 115.

The CPU 111 performs various calculation and control for realizing theprotection function of the battery cell 2 and the processing functionfor calculating the battery remaining amount by executing programsstored in a not-shown nonvolatile memory. The driver 112 outputs gatevoltage of the charge FET 121 and the discharge FET 122 under control bythe CPU 111 to drive respective FETs. The communication interfacecircuit 113 is an interface performing, for example, a serialcommunication, which is connected to an external apparatus through thecontrol terminal 35 to enable communication between the apparatus andthe CPU 111 in accordance with a prescribed format.

The A/D converting circuit 114 detects voltage at both ends of theresistance R1 inserted between the cell-side positive terminal 31 andthe charge FET 121, and voltage at the external positive terminal 33 toconvert them into digital signals to be supplied to the CPU 111. The A/Dconverting circuit 114 also converts detected values by the temperaturedetection circuit 115 into digital signals to be supplied to the CPU111. The temperature detection circuit 115 detects temperature of thebattery cell 2. As the temperature detection circuit 115, for example, acircuit in which a diode and a resistance are connected in series isprovided, and a method of detecting temperature based on variations ofvoltage of the resistance according to the temperature characteristic ofthe diode can be applied.

The charge FET 121 and the discharge FET 122, each include a MOSFET(Metal Oxide Semiconductor FET) in which a diode is built between asource and a drain equivalently, which function as protection switchesat the time of charging or discharging the battery cell 2 respectivelyunder control of the microcontroller 110. Specifically, it is possiblethat the charge FET 121 selectively shuts down charge current to thebattery cell 2 and performs charging to the battery cell 2 from thecharger at the time of conduction. The discharge FET 122 selectively canshut off discharge current of the battery cell 2 and discharge and candischarge of the battery cell 2 at the time of conduction, which enablespower supply to the apparatus.

In the battery protection circuit 3, the CPU 11 of the microcontroller110 stores an “abnormality determination flag” for managing abnormalstates of the battery cell 2 in a not-shown memory. The CPU 111 updatesthe abnormality determination flag based on voltage at both ends of thebattery cell 2 (hereinafter, referred to as a cell voltage), chargecurrent and discharge current of the battery cell 2 based on the voltageof both ends of the resistance R1, detection information of chargerstart based on the voltage detected value at the external positiveterminal 33 and information of temperature and the like detected by thetemperature detection circuit 115, performing protection operation ofthe battery cell 2 by controlling operations of the charge FET 121 andthe discharge FET 122 based on the abnormality determination flag. Also,information of abnormality detection based on the abnormalitydetermination flag can be outputted to the side of the externalapparatus through the control terminal 35. It is also possible that theCPU 111 performs calculation such as integration of charge/dischargecurrent and temperature compensation for the integrated values, andoutputs the calculated results to the side of the external apparatusthrough the control terminal 35.

Next, operation of the battery protection function in the batteryprotection circuit 3 will be explained in detail. First, FIG. 3 is aview showing transitions of control states of charge/dischargeoperations by a microcontroller.

The CPU 111 of the microcontroller 110 employs four control states whichcan be changed to one another as shown in FIG. 3, when controllingcharging/discharging operations for the battery protection. In thecontrol state A, both the charge FET 121 and the discharge FET 122 areturned on to enable both charging and discharging of the battery cell 2.In the control state B, the charge FET 121 is turned off and thedischarge FET is turned on to enable only discharging to be possible. Inthe control state C, the charge FET 121 is turned on and the dischargeFET 122 is turned off to enable only charging to be possible. In thecontrol state D, both the charge FET and the discharge FET are turnedoff to disable both charging and discharging.

Accordingly, the CPU 111 changes the state to four control states inwhich drive states of the charge FET 121 and the discharge FET 122 aredifferent, and performs appropriate battery protection operation inaccordance with abnormal states determined by the abnormalitydetermination flag by determining that the state should be changed towhich control state according to a value of the abnormalitydetermination flag which will be explained below.

FIG. 4 is a diagram showing a configuration of the abnormalitydetermination flag.

The abnormality determination flag used in the embodiment includes 8-bitflag as shown in FIG. 4, and different types of abnormal states aredefined in each bit, and information of presence/absence of respectiveabnormality occurrence can be stored individually. The CPU 111determines and set a value in each bit of the abnormality determinationflag by the following conditions at any time based on various detectioninformation inputted through the A/D conversion circuit 114. Thenumerical conditions such as voltage, current, temperature and the likeshown as follows are absolutely examples and can be appropriatelychanged according to the specification of the battery cell.

[“0” bit] The bit indicates whether the battery cell 2 is in a state ofabnormally high temperature or not. The CPU 111 sets “1” in the “0” bitwhen the temperature becomes 60 degrees or more and sets “0” when thetemperature becomes 55 degrees or less after that based on detectioninformation from the temperature detection circuit 115.

[First bit] The bit indicates whether the battery cell 2 is in a stateof abnormally low temperature or not. The CPU 111 sets “1” in thefirst-bit when the temperature becomes −50 degrees or less and sets “0”when the temperature becomes −45 degrees or more after that based ondetection information from the temperature detection circuit 115.

[Second bit] The bit indicates whether drastically large dischargecurrent flowed or not by short-circuit of the power supply terminal ofthe battery pack 1 to outside, that is, the external positive terminal33 and the external negative terminal 34 of the battery protectioncircuit 3. The CPU 111 sets “1” in the second bit when discharge currentdetected based on the voltage of both ends of the resistance R1 becomes10A or more, and sets “0” when determining that charging from thecharger is started after that. The determination conditions of chargingstart will be described later.

[Third bit] The bit indicates whether discharge current of the batterycell 2 in is an excessive “overcurrent discharge state” or not. The CPU111 sets “1” in the third bit when the discharge current becomes 3 A ormore, and sets “0” when determining that charging from the charger isstarted.

[Fourth bit] The bit indicates whether cell voltage is in an“overdischarge state” to a degree that power supply to outside is notpossible or not. The CPU 111 sets “1” in the fourth bit when the cellvoltage becomes 2.5V or less, and sets “0” when the cell voltage becomes2.52V or more.

[Fifth bit] The bit indicates whether cell voltage is in a further lower“deep discharge state” or not. The CPU 111 sets “1” in the fifth bitwhen the cell voltage becomes 2.0V or less, and sets “0” when the cellvoltage becomes 2.52V or more after that. Since operation of themicrocontroller 110 is not possible because the cell voltage is low inthe deep discharge state, the microcontroller 110 is actually shut downwhen the bit “5” is on.

[Sixth bit] The bit indicates whether charge current of the battery cell2 is in an excessive “overcurrent charge state” or not. The CPU 111 sets“1” in the sixth bit when charge current becomes 3 A or more, and sets“0” when determining that discharge is started by a discharge load beingconnected after that. The discharge start is detected when dischargecurrent becomes 150 mA or more which is calculated based on the voltageat both sides of the resistance R1.

[Seventh bit] The bit indicates whether cell voltage is in an“overcharge state” in which the cell voltage is too high and dangerous.The CPU 111 sets “1” in the seventh bit when the cell voltage becomes4.2V or more, and sets “0” when the cell voltage becomes 4.1 V or lessafter that.

As described above, in the abnormality determination flag,presence/absence of abnormal states concerning temperature are stored bythe “0” bit and the first bit,

presence/absence of abnormal states concerning discharging are stored bythe second bit to the fifth bit, and presence/absence of abnormal statesconcerning charging are stored by the sixth bit and the seventh bit. Asfor the abnormal states concerning discharging and charging, respectivepresence/absence of abnormal states caused by voltage andpresence/absence of abnormal states caused by current are storedindividually. Therefore, the type of abnormality occurring at presentcan be identified meticulously and accurately, and also in the case thatdifferent types of abnormalities occur, types can be identified easily.Accordingly, only by referring the abnormality determination flag, theoptimum protection operation control according to the identified resultscan be executed.

In the determination in the second bit and the third bit, the chargestart is detected when at least one of the following two conditions issatisfied. The first condition is a case in which voltage of theexternal positive terminal 33 becomes 3.0 or more. The second conditionis a case in which charge current detected based on the voltage of bothends of the resistance R1 becomes 150 mA or more.

Here, in related arts, the charge start was determined only based on thevoltage of the external positive terminal 33, However, in the case thatthe discharge FET 122 is on and the cell voltage decreases, when thecharger is connected to the battery pack 1, the voltage of the chargersometimes decreases involved by the cell voltage. In such case, it issometimes incapable of detecting the charge start. In the embodiment,the charge start can be detected based on not only the voltage of theexternal positive terminal 33 but also a detected value of chargecurrent. Since charge current flows even when the voltage of the chargerdecreases as described above, the charge start can be detected morepositively by detecting the charge current. Therefore, in theovercurrent discharge state or in the case in which the power supplyterminal of the battery pack 1 is short circuited, operation can bereturned positively when charging is started.

Next, transition conditions of control states according to theabnormality determination flag will be explained. FIG. 5 is a diagramshowing correspondence between values of the abnormality determinationflag and control states.

First, when all bits of the abnormal determination flag are “0”, the CPU111 makes a transition to the control state A, turning on both thecharge FET 121 and the discharge FET 122. That is, since no abnormalityis detected at this time, the battery cell 2 is allowed to be in a statein which both charging and discharging are possible.

When the “0” bit to the fifth bit are all “0” and at least one of thesixth bit and the seventh bit is “1”, the CPU 111 makes a transition tothe control state B and turns on only the discharge FET 122. That is,since the charge voltage is excessive or excessive charge current flowsat the time, the battery cell 2 is allowed to be a state in whichcharging is not possible.

When all bits of the “0” bit, the first bit, the sixth bit and theseventh bit are “0” and at least one of the second bit to the fifth bitis “1”, the CPU 111 makes a transition to a control state C and turns ononly the charge FET 121. That is, since some abnormality is detectedwith respect to the discharge state at the time, the battery cell 2 isallowed to be in a state in which discharge is not possible, namely, inwhich power supply to the apparatus is not possible.

When at least one of the second bit to the fifth bit is “1” and at leastone of the sixth bit and the seventh bit is “1”, the CPU 111 makes atransition of the control state D and both the charge FET 121 and thedischarge FET 122 are turned off. That is, abnormalities are detected atboth of the charge state and the discharge state at the time and it isconceivable that the normal operation is not possible, therefore, thebattery cell 2 is allowed in a state in which neither charging nordischarging are possible.

In the case that at least one of the “0” bit and the first bit is “1”,the CPU 111 makes a transition to the control state D and turns off boththe charge FET 121 and the discharge FET 122 regardless of values in thesecond bit to the seventh bit. That is, it is determined that thebattery cell 2 is in a dangerous state because it becomes high intemperature, or in a state in which the normal operation is not possiblesuch that the cell voltage decreases due to low temperature, therefore,the battery cell 2 is forcibly allowed to be in the unavailable stateregardless of charging and discharging states.

As described above, the optimum protection operation control accordingto the occurrence situation of abnormal states can be executed at anytime by associating values of the abnormality determination flag and thecontrol states. Particularly, an appropriate transition destinationaccording to identified results can be determined by simple processingwhile various types of abnormal states can be identified. Furthermore,when any type of abnormal state is returned to the normal state, it ispossible that the state makes a transition to the appropriate controlstate at any time.

For example, in the abnormal state concerning charging, only theovercharge state based on the detected value of charge voltage wasdetermined in the related arts, however, in the embodiment, it is alsopossible to determine overcurrent charge state based on the detectedvalue of charge current in addition to the overcharge state. The returnfrom the overcurrent charge state should be performed by the detectionof discharge based on charge current, which is different from theovercharge state, however, the appropriate return operation can beexecuted only by updating the abnormality determination flag, applyingsuch right return condition. In addition, not only abnormal states basedon detected values of voltage and current but also abnormal states basedon the detected value of temperature can be determined.

Even when the detection types of abnormal states increase as describedabove, the transition destination of the control state can be determinedand the appropriate protection operation can be executed at any timeonly by providing bits corresponding to the detection types in theabnormality determination flag and by prescribing correspondence betweencombination in the flag and control states. Even when plural types ofabnormalities are detected in any combination, the control state to bechanged can be determined, therefore, accurate response is possible withrespect to various abnormal states as well as returning operation fromthe state can be appropriately executed. As a result, secure protectionoperation can be executed at any time, which increases safety.

Since various types of abnormal states at present are usually stored inthe abnormality determination flag, the current abnormal state can beimmediately known by the abnormality determination flag being allowed tobe read out from outside through the control terminal 35, as a result,failure analysis can be executed efficiently. For example, when somechange of operation occurs such that charging operation or dischargeoperation stops in an inspection before shipment, an inspector cananalyze the cause of occurrence of abnormality immediately andaccurately, which was occurred in the battery pack 1 by reading out theabnormality determination flag. Even when histories of abnormalityoccurrence are not stored, it is possible to find which kind ofabnormality occurrence caused the change of operation, therefore, themerits such as reduction of a memory region in the battery protectioncircuit 3 and increase of processing efficiency can be obtained inaddition to the increase of failure analysis efficiency.

Next, FIG. 6 is a diagram showing a configuration of a battery packaccording to a second embodiment of the invention. In FIG. 6, functionscorresponding to ones in FIG. 2 are shown by putting the same numeralsand signs, and explanations thereof will be omitted.

The battery pack shown in FIG. 6 includes two battery cells, namely, abattery cell 2 a and a battery cell 2 b. A negative terminal 22 a of thebattery cell 2 a and a positive terminal 21 b of the battery cell 2 bare connected through a cell-side negative terminal 32 a and a cell-sidepositive terminal 31 b of a battery protection circuit 3 a, accordingly,the battery cell 2 a and the battery cell 2 b are connected in series.In addition, a cell-side positive terminal 31 a and a cell-side negativeterminal 32 b of the battery protection circuit 3 a are connected to apositive terminal 21 a of the battery cell 2 a and a negative terminal22 b of the battery cell 2 b, respectively.

The CPU 111 of the battery protection circuit 3 a is capable ofdetecting voltage between the cell-side positive terminal 31 a and thecell-side negative terminal 32 b, namely, voltage between two batterycells 2 a and 2 b connected in series, charging and discharging currentthrough the A/D converting circuit 114. In addition, the cell-sidenegative terminal 32 a and the cell-side positive terminal 31 b are alsoconnected to the A/D converting circuit 114, accordingly, respectivevoltages of the battery cells 2 a and 2 b can be detected. The CPU 111sets abnormality determination flags for the respective battery cells 2a and 2 b according to the voltages, currents and temperatures of therespective battery cells 2 a and 2 b, which are detected by thetemperature detection circuit 115.

FIG. 7 is a diagram showing abnormality determination flagscorresponding to respective two battery cells.

As shown in FIG. 7, types of abnormal states stored in the abnormalitydetermination flag corresponding to each of two battery cells 2 a and 2b are the same as the first embodiment using one battery cell. Thesetting conditions of values concerning each bit are also the same. Itshould be noted that the abnormal state concerning temperature isdetermined based on detected values of temperature in respective batterycells 2 a and 2 b, and the overdischarge state, the deep discharge stateand the overcharge state are determined based on detected values ofvoltage in respective battery cells 2 a and 2 b.

The CPU 111 provisionally determines that the respective battery cells 2a and 2 b should make a transition to which control states A to D baseon respective abnormality determination flags. Then, as explained inFIG. 8, the conclusive transition destination is determined according tocombination of control states provisionally determined concerningrespective cells and operations of the charge FET 121 and the dischargeFET are controlled.

FIG. 8 is a chart showing transition conditions of control statesaccording to abnormal states of respective battery cells.

As shown in FIG. 8, when control states provisionally determined by theabnormality determination flags corresponding to the battery cells 2 aand 2 b respectively are the same, the CPU 111 makes a transition tothat control state. In the case that abnormality is not detected fromone of the abnormality determination flag and the transition destinationis provisionally determined to be the control state A, when someabnormality is detected by the other abnormality determination flag, theCPU makes a transition to the control state based on the otherabnormality determination flag.

When some abnormality is detected by both abnormality determinationflags and control states provisionally determined by respectiveabnormality determination flags are different from each other, the stateis allowed to be changed to the control state D. That is, abnormalityconcerning charging occurs at one side of the battery cells 2 a and 2 band abnormality concerning discharging occurs at the other side in thiscase, therefore, the safety of respective battery cells 2 a and 2 b canbe secured by stopping both charging and discharging. In the case that,for example, abnormality in one battery cell is cancelled earlier, thestate is allowed to be changed to the control, state corresponding tothe other abnormality. Accordingly, even when different types ofabnormalities occur at respective battery cells, or when theseabnormalities are cancelled, appropriate protection operation can bepositively executed at any time.

Furthermore, in the case that not only two battery cells such as in thesecond embodiment but also further more battery cells are connected, inseries, abnormality determination flags corresponding to respectivebattery cells are set, and the conclusive control state is determinedaccording to combination of control states provisionally determinedbased on the flags, thereby executing appropriate protection operationat any time. That is, when abnormalities are detected from pluralabnormality determination flags, if control states provisionallydetermined from these flags are the same, the state is changed to thatcontrol state, and if control states provisionally determined aredifferent, the state is changed to the control state D. Also in the casethat at least one of the control states provisionally determined is thecontrol state D, the state is changed to the control state D.Furthermore, in the case that plural battery cells are connected inparallel, appropriate protection operation can be executed by the sameprocessing. Accordingly, the method of providing abnormalitydetermination flags corresponding to respective battery cells anddetermining the control state based on these abnormality determinationflags can be applied to the protection operation for various forms ofbattery packs without changing a basic control procedure.

1. A battery pack in which a processing circuit executing protectionprocessing for abnormality occurrence of a secondary battery is housedwith the secondary battery, comprising: a discharge current shut-offcircuit selectively shutting off discharge current of the secondarybattery; a charge current shut-off circuit selectively shutting offcharge current of the secondary battery; a voltage detection unitdetecting voltage between a positive terminal and a negative terminal ofthe secondary battery; a current detection unit detecting magnitude ofcharge and discharge current of the secondary battery; an abnormal statedetermination unit determining presence/absence of plural abnormalstates at any time, which include at least an overcharge state and anoverdischarge state based on detected results by the voltage detectionunit as well as an overcurrent charge state and an overcurrent dischargestate indicating that charge current and discharge current are excessiverespectively based on detected results by the current detection unit,and storing determination information indicating a determination resultat that time; and a protection processing unit controlling respectiveoperations of the discharge current shut-off circuit and the chargecurrent shut-off circuit based on the determination information.
 2. Thebattery pack according to claim 1, wherein the protection processingcircuit includes four control states according to combinations ofshut-off/conductive states of the respective discharge current shut-offcircuit and the charge current shut-off circuit.
 3. The battery packaccording to claim 1, wherein the abnormal state determination unitstores respective determination results of presence/absence of pluralabnormal states as a flag, and wherein the protection processing unitcontrols respective operations of the discharge current shut-off circuitand the charge current shut-off circuit according to combination ofvalues in the flag.
 4. The battery pack according to claim 1, whereinthe protection processing unit allows only charge current shut-offcircuit to be shut off when determined that the state is the overchargestate or the overcurrent charge state as well as determined that thestate is neighter the overdischarge state nor the overcurrent dischargestate, and allows only the discharge current shut-off circuit to be shutoff when determined that the state is the overdischarge state or theovercurrent discharge state as well as determined that the state isneigher the overcharge state nor the overcurrent charge state based onthe determination information.
 5. The battery pack according to claim 4,wherein the protection processing unit allows both the discharge currentshut-off circuit and the charge current shut-off circuit to be shut offwhen determined that the state is the overcharge state or theovercurrent charge state as well as determined that the state is alsothe overdischarge state or the overcurrent discharge state based on thedetermination information.
 6. The battery pack according to claim 1,further comprising: a charge detection means for detecting the chargestart based on voltage between charge terminals for connecting to anexternal charger, and wherein the abnormal state determination unit,after determining that the state is the overcurrent discharge state andupdating the determination information, determines that the overcorrentdischarge state is cancelled and updates the determination informationwhen the charge start is detected by the charge detection means or whencharge current of more than a prescribed value is detected by thecurrent detection unit.
 7. The battery pack according to claim 1,wherein the abnormal state determination unit, when charge current whichis more than a first reference value is detected by the currentdetection unit, determines that the state is the overcurrent chargestate and updates the determination information, then, when dischargecurrent which is more than a second reference value is detected,determined that the overcurrent charge state is cancelled and updatesthe determination information.
 8. The battery pack according to claim 1,further comprising: a temperature detection unit detecting temperatureinside the secondary battery, and wherein the abnormal statedetermination unit determines an abnormal high temperature state and anabnormal low temperature state respectively indicating that the state isabnormally high in temperature and abnormally low in temperature basedon detection results by the temperature detection unit, and storingdetermination results by the determination information, and wherein theprotection processing unit allows both the discharge current shut-offcircuit and the charge current shut-off circuit to be shut off whendetermined that the state is the abnormally high temperature state orthe abnormally low temperature state based on the determinationinformation, regardless of other determination results in thedetermination information.
 9. The battery pack according to claim 1,further comprising: a charge detection unit detecting whether chargingto the secondary battery is started or not, and wherein the abnormalstate determination unit determines that the state is the overcurrentdischarge state when discharge current detected by the current detectionunit is smaller than a first reference value as well as determines thatthe state is a short-circuit state in which the positive terminal andthe negative terminal of the secondary circuit are short circuited whenthe discharge current is smaller than a second discharge current whichis lower than the first reverence value, and manages presence/absence ofthe short-circuit state in addition to the overcurrent discharge statein the determination information, then, after determining as theshort-circuit state, when charge start is detected by the chargedetection unit, the abnormal state determination unit determines thatthe short-circuit state is cancelled and updates the determinationinformation.
 10. The battery pack according to claim 1, wherein pluralsecondary batteries are included in the same battery pack, wherein thevoltage detection unit detects voltage between the positive terminal andthe negative terminal at each secondary battery, wherein the abnormalstate determination unit stores determination results of the abnormalstates of each secondary battery as individual determinationinformation, wherein the protection processing unit controls respectiveoperations of the discharge current shut-off circuit and the chargecurrent shut-off circuit according to combinations of determinationresults of the abnormal states in respective determination information.11. The battery pack according to claim 10, wherein the protectionprocessing unit, when it is indicated that there is an abnormality inone determination information and it is indicated that there is not anabnormality in other determination information, controls respectiveoperations of the discharge current shut-off circuit and the chargecurrent shut-off circuit based on the determination informationdetermined that there is the abnormality.
 12. The battery pack accordingto claim 10, wherein the protection processing unit, when it isindicated that the state is the overcharge state or the overcurrentcharge state in one determination information and it is indicated thatthe state is the overdischarge state or overcurrent discharge state inother determination information, allows both the discharge currentshut-off circuit and the charge current shut-off circuit to be shut off.13. The battery pack according to claim 10, wherein the protectionprocessing unit includes four control states according to respectivecombinations of shut-off/conductive states of the discharge currentshut-off circuit and the charge current shut-off circuit, and afterdetermining transition destinations of the control states provisionallybased on respective determination information, determines a conclusivetransition destination according to combinations of the control stateswhich were provisionally determined.
 14. The battery pack according toclaim 13, wherein the protection processing unit, when all controlstates which were provisionally determined based on respectivedetermination information are the same, determines the conclusivetransition destination as that control state, when at least one of thecontrol states which were provisionally determined makes at least one ofthe discharge current shut-off circuit and the charge current shut-offcircuit be a shut-off state and remaining control states except thatcontrol state make both the discharge current shut-off circuit and thecharge current shut-off circuit be a conductive state, determines theconclusive transition destination as the control state including theshut-off state, and when at least one of the control states which wereprovisionally determined makes one of the discharge current shut-offcircuit and the charge current shut-off circuit be the shut-off stateand at least one of the remaining control states makes the other of thedischarge current shut-off circuit and the charge current shut-offcircuit be the shut-off state, as well as at least one of the controlstates which were provisionally determined makes both the dischargecurrent shut-off circuit and the charge current shut-off circuit be theshut-off state, determined the conclusive transition destination as thecontrol state which makes both the discharge current shut-off circuitand the charge current shut-off circuit be the shut-off state.
 15. Abattery protection method for protecting a secondary battery whenabnormality occurs, comprising the steps of: determiningpresence/absence of plural abnormal states by an abnormal statedetermination unit, which includes at least an overcharge state and anoverdischarge state based on detected results of voltage between apositive terminal and a negative terminal of the secondary battery by avoltage detection unit as well as an overcurrent charge state and anovercurrent discharge state indicating that charge current and dischargecurrent are excessive respectively based on detected results of chargeand discharge current of the secondary battery by a current detectionunit and storing determination information indicating determinationresults at that time; and controlling respective operations of adischarge current shut-off circuit selectively shutting off dischargecurrent of the secondary battery and a charge current shut-off circuitselectively shutting off charge current of the secondary battery by aprotection processing unit based on the determination information.